The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

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Flood watch warnings remain in place for at least seven rivers up to the NSW Northern Rivers region, with SES NSW operations commander Greg Murphy earlier stating the Tweed, Wilsons, Richmond and Brunswick rivers were of most concern.

"The best information is that we could be in for another couple of hundred millimetres of rain so the flood emergency isn't over yet," he told the TODAY Show this morning.

"If the river continues to rise with additional rain, low-lying properties could be affected and... there is potential for more flooding."

Weatherzone meteorologist Brett Dutschke said the main area of concern was between the Tweed region and Coffs Harbour.

“There’s been widespread totals of between 150 and 300mm in two days,” Mr Dutschke said.

“At this stage, it looks unlikely there’ll be major flooding and evacuations but we are expecting about 50 to 100mm over the next few days.”

As of last night, more than 210mm of rain had fallen on the Richmond and Wilsons River during the weekend.

Evans Head and Yamba also recorded totals of 200mm or more.

As people began to head home after the long weekend, Mr Murphy warned them to take extra care in avoiding floodwaters.

"Take it easy on the roads. Long weekends are very busy. Don't drive through floodwaters, water is still travelling quite fast.